1. Field of the Invention
This invention relates to word processing systems and more particularly to the selection of correct keyboard character sets during block transfer of stored text.
2. Description of Prior Art
Prior art relating to the present invention includes:
(a) The IBM OS/6 system uses an 8-bit extension of the 7-bit magnetic card code, but this does not have enough code points to represent all possible supported graphics. In order to maintain the correct keyboard character set for the input graphics it uses a combination of two techniques. The keyboard number representing the keyboard character set which received the text input is saved in a Document Master Format. This is operator selectable. But, where there is a keyboard character set change within a document a format change is inserted in which each character or a short phrase is imbedded within a 6-byte sequence. The problems with this approach are that the operator must either find and inspect the prior format, or must remember what input keyboard has been active in order to know which key to press for a given graphic. Further, the 6-byte sequences inefficiently utilize the available storage for words and phrases especially in limited areas such as margin text. Should the operator make a change in the keyboard specified by the Document Master Format the printed/displayed text could change since the code points within text had not been translated to reflect the change in the specified keyboard in the master format.
(b) The IBM 5520 system adopted the Multi-Lingual EBCDIC Code Page 256 to be the internal text representation. Each of the characters within this Code Page is self-defining but can be ambiguous with characters in other Code Pages. A serious problem in this regard is that communication between the model 5520 and other devices, such as the OS/6, are made difficult since there is no keyboard character set representation within the data stream.